The U.S. and U.K. on Saturday conducted another round of airstrikes against military targets controlled by Iran-backed Houthi rebels in Yemen, both countries' defense secretaries announced.

Why it matters: This is the fourth round of US-UK strikes against the Houthis amid continuous attacks by the rebel group against commercial vessels in the Red Sea.

• The U.S. and U.K. had support of Australia, Bahrain, Canada, Denmark, the Netherlands and New Zealand, U.S. Defense Secretary Lloyd Austin said in a statement.
• Austin said the militaries targeted eight locations, including underground weapons storage facilities, missile storage facilities, one-way attack unmanned aerial systems, air defense systems, radars and a helicopter.
• "These precision strikes are intended to disrupt and degrade the capabilities that the Houthis use to threaten global trade, naval vessels, and the lives of innocent mariners in one of the world's most critical waterways," the countries supporting the strikes said in a joint statement.

What they're saying: "The United States will not hesitate to take action, as needed, to defend lives and the free flow of commerce in one of the world's most critical waterways," Austin said.

• "We will continue to make clear to the Houthis that they will bear the consequences if they do not stop their illegal attacks, which harm Middle Eastern economies, cause environmental damage, and disrupt the delivery of humanitarian aid to Yemen and other countries," Austin continued.

UK Defense Secretary Grant Shapps echoed Austin on the "severe" Houthi attacks against ships in the Red Sea. He said they affected British-owned MV Islander and the MV Rubymar, which led the crew to abandon the ship.

• "It is our duty to protect lives and sea and preserve freedom of navigation," Shapps said.

The other side: The Houthi rebels said in a statement they will respond to the "American and British escalation" with more attacks against targets in the Red Sea.

• The Houthis said they attacked a U.S. oil tanker in the Gulf of Aden with precision missiles.

Flashback: The Biden administration earlier this year re-designated the Houthi rebels as a foreign terrorist organization after multiple attacks by the militant group on ships in the Red Sea.

• The U.S. and U.K. launched the first round of airstrikes in early January.

Between the lines: The escalation in the Red Sea and the growing U.S. military involvement comes amid fears that tensions heightened by the Israel-Hamas war could boil over into a larger regional conflict.

• The Houthis have said they began the attacks in an effort to get the Israeli military to halt its offensive in Gaza.

Go deeper: What to know about Yemen's Houthi rebels and the Red Sea conflict